1. Field of the Invention
The present invention relates to electric power systems, and more particularly to a method and apparatus for connection of multiple power supply inputs, and for soft-switching during hot swap of modules for AC and DC electric power systems.
2. Description of the Related Art
Electric systems used in complex environments such as aerospace systems, more electric aircraft systems, industrial environments, vehicles, etc., include a large number of electric modules. Various electric modules may need to be extracted and replaced with other modules, to change functionality or to replace modules that exhibit faults.
Hot swap, hot-plug, and hot-dock are terms used interchangeably to refer to the process of safely inserting or removing cards, PC boards, cables, and/or modules from a host system without removing power. The goal of hot swap is to insert or remove modules without disturbing, damaging, or degrading up/down-stream adjacent line replaceable modules/subsystems, to increase system availability, reduce down time, simplify system repair, and allow for system maintenance/upgrade without interrupting service to other loads.
Electric modules included in environments such as aerospace systems, more electric aircraft systems, industrial environments, vehicles, etc., may be connected to multiple power supply voltage inputs, and extract one voltage output to be used by the modules. During hot swap of electrical modules, the multiple power supply voltage inputs are also connected or disconnected from the host system, or from the removable electrical modules, without removing power.
If not designed for properly, hot swap can cause severe electrical, mechanical, thermal and operational problems in an electrical system. For example, pulling a board/module out while there is current passing through the module connectors, or inserting a board/module with all bulk/bypass capacitors at zero volts, can introduce severe electrical voltage/current transients which may adversely impact reliability and lead to safety consequences. Current chopping introduces Ldi/dt variations (where L is inductance of a load, for example) leading to very large voltage transients which are a major safety concern for maintenance people, as large voltage transients can cause high voltage electrical shock.
One problem with typical/conventional techniques for hot-swap is a lack of proper connection of multiple power supply voltage inputs for a voltage output for replaceable modules. Typical/conventional methods use passive diode-ORing systems to connect multiple power supply voltage inputs to a supply bus for replaceable modules. Such passive diode-ORing systems result in excessive power losses and voltage drops. Significant voltage drops, particularly when preferred paths of power consumption from AC and DC sources are required, are a major problem. Current chopping occurring during insertion or extraction of modules is a major contributor to excessive voltage/current transients that stress and damage individual components and reduce the Mean Time Between Failure (MTBF) for the host system and for the removable modules.
A number of publications have studied ORing systems for electrical modules. One such system is described in U.S. Pat. No. 6,891,425 B1 titled “Low Voltage OR'ing Circuits and Methods with Zero Recovery Time” by Thong Huynh. The system described in this patent includes a MOSFET coupled between a power supply and a load, a controller that senses the current through the MOSFET and turns the MOSFET off when the current falls below a predetermined threshold current, and a second MOSFET adding hot swap capability. This circuit, however, does not protect against transient voltages/currents when a board is taken-out from a motherboard/backplane. Moreover, the second MOSFET is designed to work both in the switch mode and in the linear mode. Because the second MOSFET has to operate both in the switch mode and in the linear mode, the linear range is narrow, which, together with typical variations in threshold voltage Vth, make the control of the second MOSFET in the linear mode hard to reproduce.
A disclosed embodiment of the application addresses these and other issues by utilizing a method and apparatus for integrated active-diode-ORing and soft power switching. The method and apparatus achieve proper connection of multiple power supply voltage inputs to realize a fault tolerant power supply bus for replaceable modules. The method and apparatus provide soft power-up/down capability during hot swap of modules for AC and DC electric power systems. The method and apparatus provide a single power bus from multiple power supply inputs, with minimum voltage drop, improved efficiency, and no looses in passive diodes. The method and apparatus provide integrated soft-switching that reduces turn-on in-rush current during board/module insertion and further eliminates current-chopping during interruption of current in inductive circuits. The method and apparatus can be used for both low and high power systems.